In general, an engine uses gasoline or diesel as fuel, nitrogen oxide (NOx) is included in exhaust gas and discharged when fuel is combusted and exhaust gas is discharged.
Because nitrogen oxide causes environmental pollution, a technology for inhibiting the nitrogen oxide from being generated is being developed, and as the technology, there is an exhaust gas recirculation (EGR) system.
The exhaust gas recirculation system is known as a technology which reduces a concentration of oxygen by mixing a part of exhaust gas with air for combustion, and prevents a flame temperature from being rapidly raised, thereby inhibiting the nitrogen oxide from being generated.
Meanwhile, a turbocharger may be installed in the engine. In the turbocharger, a turbine and a compressor are connected to each other by a single shaft, the turbine of the turbocharger is rotated by energy (temperature and pressure) of exhaust gas, and the compressor is driven by rotational force of the turbine. The compressed air is mixed with a larger amount of fuel, thereby improving efficiency of the engine.
On the other hand, a pressure wave (or pressure pulse), which is propagated when an exhaust valve of a cylinder is opened, may act as back pressure for other cylinders. There is a problem in that the aforementioned back pressure interference action degrades performance of the exhaust gas recirculation system.
In order to inhibit the exhaust gas interference, a twin-entry layout, which has two independent passages at a portion where exhaust gas flows into the turbine from an exhaust manifold, is known to be applied.
In the exhaust gas recirculation system, when recirculating gas is obtained from only one exhaust manifold, imbalance in pressure and flow rate between two lines leading to the turbine is caused, which degrades overall performance of the turbine and the engine system.
On the other hand, in a case in which the turbocharger, to which the twin-entry layout is applied, and the exhaust gas recirculation system are applied together, the recirculating gas is generally obtained from both the exhaust manifolds. However, in a case in which a phenomenon that exhaust pressures waves are exchanged through both the exhaust manifolds is not effectively inhibited, there is a problem in that back pressure is increased such that performance of the exhaust gas recirculation system deteriorates.
On the other hand, there is an example in which the twin-entry layout is applied to the exhaust gas recirculation system, and recirculating gas is obtained from two recirculation lines. Valves are installed in the two recirculation lines, respectively, thereby inhibiting the back pressure exchange phenomenon. However, in this example, since additional valves need to be installed and designed, there is a problem in that costs are increased.
There is another exhaust gas recirculation system for solving the aforementioned problem, and the exhaust gas recirculation system in the related art will be described with reference to the attached FIG. 1.
A plurality of cylinders is disposed in an engine 10, and the cylinders may be designated as a first cylinder group 12a and a second cylinder group 12b. First and second exhaust manifolds 21 and 22 are connected to the first cylinder group 12a and the second cylinder group 12b, respectively. The first and second exhaust manifolds 21 and 22 are connected to a turbine 30 of a turbocharger.
That is, exhaust gas discharged from the first and second cylinder groups 12a and 12b is provided to the turbine 30 through the first and second exhaust manifolds 21 and 22.
The turbine 30 is connected to a compressor 40, the turbine is driven by energy of exhaust gas, and driving power drives the compressor 40 to compress air.
Meanwhile, a first recirculation line 51 and a second recirculation line 52 are connected to the first exhaust manifold 21 and the second exhaust manifold 22, respectively, such that a part of exhaust gas is obtained.
The other side of each of the first and second recirculation lines 51 and 52 is connected to a pulse converter unit 60. The pulse converter unit 60 serves to shut off a reverse flow and an exchange phenomenon of the exhaust pressure wave.
That is, exhaust gas, which circulates through the first recirculation line 51, and exhaust gas, which circulates through the second recirculation line 52, are combined in the pulse converter unit 60.
A combining recirculation line 70 is connected to the pulse converter unit 60, a cooler 90 is connected to the other side of the combining recirculation line 70, and a valve 80 is provided on the combining recirculation line 70. The valve 80 inhibits a back pressure exchange phenomenon. The cooler 90 cools high-temperature exhaust gas.
The exhaust gas cooled by the cooler 90 is sent to a mixer where air and fuel are mixed.
However, the exhaust gas recirculation system in the related art illustrated in FIG. 1 has a complicated structure, and as a result, there is a problem in that manufacturing costs are increased.
In addition, in order to improve efficiency of the engine, it is necessary to additionally increase an amount of intake air, and it is necessary to further improve fuel efficiency.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.